This invention relates to a rotating drum for use in a magnetic storage system in which read and write operations are effected using the rotating drum. Examples of such magnetic storage system include a video tape recorder (VTR), a mass storage system (MSS) and a data recorder in which a magnetic head is moved relative to and into contact with a magnetic recording medium to effect read and write operations. Such a rotating drum is also used in a magnetic-recording characteristics measuring system in which a magnetic recording medium is moved relative to and into contact with a fixed magnetic head to effect read and write operations. More particularly, the invention relates to the structure and shape of such a drum which ensure stable read and write characteristics.
There have been widely used magnetic recording systems in which a magnetic recording medium is wound around a rotating drum, and read and write operations are effected by a magnetic head. A typical example of such magnetic recording systems is a video tape recorder (VTR). The advantage of the rotating drum is that a relative speed between the magnetic head and the magnetic recording medium can be increased while keeping the system to a small size.
In the magnetic recording system having such a rotating drum, in order to stabilize read and write characteristics, it is very important to maintain a good condition of contact between the magnetic head and the magnetic recording medium. For this reason, a magnetic recording medium-winding surface (i.e., outer peripheral surface) of the drum is quite precisely finished or worked with respect to roundness and surface roughness. At present, an aluminum alloy is usually used as a material constituting a rotating drum device. The reason for this is that an aluminum alloy is lightweight and has a high machinability and non-magnetic properties. On the other hand, an aluminum alloy is disadvantageous in that it has a relatively low rigidity and therefore is liable to be deformed when subjected to an external or applied force.
FIG. 5 is a bird's eye view of a conventional rotating drum, and FIG. 6 is a top plan view of the conventional drum, and FIG. 7 is a sectional view of the conventional drum. As shown in these Figures, an opening or notch (window) 2 for projecting a magnetic head is formed through the peripheral wall of the drum. Examples of rotating drums having such an opening or notch are disclosed in Japanese Laid-Open (Kokai) Patent Application No. 55-101132/(A) and Japanese Laid-Open Utility Model Application No. 56-2162/(A).
In the case of a rotating drum of the type containing a magnetic recording medium, the above-mentioned opening or notch serves as a window for pulling out the magnetic recording medium. Because of the provision of such an opening or notch, the drum is subjected to irregular deformation when the drum is rotated, so that the recording medium-winding surface of the drum becomes out of a uniform circular shape. As a result, the contact between the magnetic head and the magnetic recording medium becomes unstable. In currently-available video tape recorders etc., the rotation frequency (rotational speed) of the drum is about 2,000 rpm, and the relative speed between the magnetic head and the magnetic recording medium is about 10 m/sec. Therefore, actually, the influence of the drum deformation on the read and write characteristics is small. However, as the recording frequency increases as a result of a higher picture resolution and a higher recording density, the required relative speed becomes higher. Therefore, it is indispensable to increase the rotation frequency of the drum in which case the centrifugal force is increased in proportion to the square of the relative speed. As a result, the deformation of the drum can not be disregarded. On example of such situation will be described below.
FIG. 8 shows results of measurements of deformation of a magnetic recording medium-winding surface 3 of the conventional rotating drum of FIGS. 6 and 7 at various rotation frequencies of the drum. The medium-winding surface 3 of this conventional rotating drum had a diameter 7 of 110 mm (i.e., a radium of 55 mm), and the diameter 8 of an inner peripheral surface 4 was 88 mm, and a height 9 of the rotating drum was 50 mm, and a depth (h) 15 of the inner peripheral surface of the rotating drum extending between the upper end of the drum and the inner bottom surface was 35 mm. The opening 2 formed through the peripheral wall of the rotating drum had a width (w) 14 of 10.5 mm in the circumferential direction of the drum, and a height of 8 mm. When the rotating drum is rotated, the amount of radial displacement of the medium-winding surface 3 starting from the state of response of the drum (that is, a variation in the distance between the medium-winding surface 3 and the center or axis 6 of rotation of the drum) increases as the rotation frequency increases, as shown in FIG. 8. However, a practical problem to be noted is the amplitude of deformation of the medium-winding surface 3 within the overall circumference. This deformation amount reaches 5 to 6 .mu.m at 5,000 rpm, and as large as 25 .mu.m at 10,000 rpm. In such condition, the contact between the magnetic head and the magnetic recording medium is quite unstable, and therefore signals can not be read and written in a stable manner.
As described above, in the conventional rotating drum, there is not provided any means for dealing with the increase of stresses developing during a high-speed rotation of the rotating drum. Therefore, the rotating drum is subjected to irregular deformation at a high-speed rotation frequency, which results in a problem that a stable contact between the magnetic head and the magnetic recording medium can not be maintained.